Photovoltaic design and many other interesting chemical problems require a method to predict and understand rates of transition between electronic states. Our group builds semiquantitative atom-centered models for the energetic fluctuations which are responsible for electronic transitions, and uses them to predict and interpret transient absorption spectra. We will discuss the outcomes of several applications of the technique to benchmark organic systems, and integration of dissipation and relaxation into typical theories of electronically excited states. The first part of the talk will discuss Lead-Halide perovskites (PbX3CH3NH3), and our combination of high quality GW-BSE excited state calculations with golden rule kinetic estimates to interpret and predict the transient population of bright states in this material. Our results corroborate the three band model proposed to understand the picosecond transient absorption experiments, but suggest additional pathways and give atomic structural information about the relaxation process.<br/><br/>In the second part of the talk, I'll discuss our ongoing efforts to unite theories of excited states (CIS,TDDFT and others) with theories of dissipation and relaxation on the single-electron level. I'll describe the agreement our models can achieve with experimental measurements of relaxation processes, and also some outstanding issues related to the treatment of Fermionic statistics in relaxation processes. Time permitting I'll talk about some of our work on the kinetics of the singlet fission process and the interesting distinction in this problem between rate theories built on transition state theory, and those built on the golden rule.

Cheap models for electronic transitions and their application to lead-halide perovskites

249th National Meeting (2015)

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